The present invention is directed to an electrolyte capacitor.
Such capacitors are usually composed, for example, of at least two foils of a valve metal (for example, aluminum) that are wound about one another. The foil serving as an anode is provided with an oxide layer which acts as a dielectric, this oxide layer being applied onto the foil in an electrochemical process. In order to increase the capacitance, the foil can be roughened, also in an electrochemical process, before the formation of the oxide layer. Spacers that are saturated with an operating electrolyte are situated between the anode and cathode foils.
When, for example, such capacitors are operated in switched power packed parts as low-voltage electrolyte capacitors, they must have especially low equivalent series resistances (ESR). The equivalent series resistance is the ohmic part in the equivalent series circuit. A high conductivity of the operating electrolyte is an important prerequisite for providing low ESR values. Moreover, the electrolyte must be compounded such that a continuous operation at .gtoreq.105.degree. C. is possible.
Extremely high conductivities up to 15 m.sup.s /cm (30.degree. C.) are obtained, for example, with ammonium salts of multi-valent, organic acids in ethyleneglycol-water mixtures. The water part of this electrolyte, however, is so high that the capacitors fail due to corrosion at operating temperatures &gt;85.degree. C.
However, such high conductivities can also be established when amides of short-chain, mono-valent acids are used as solvents. Water can thereby be entirely or partially eliminated. The main examples of such acid amides are N, N-dimethyl formamide (DMF) and N, N-dimethyl acetamide (DMAC).
It must thereby be taken into consideration, however, that most amides are hazardous substances that are injurious to health. Thus, the maximum work place concentration quotients for DMF or, respectively, DMAC amount to only 20 or, respectively, 10 ppm. Moreover, DMF and DMAC are suspected of being carcinogenic and teratogenic.